(1) Field of the Invention
The present invention relates generally to tracking systems and, more particularly, to tracking systems and methods for tracking in real time the trajectory and velocity of underwater objects which may be traveling at high speeds utilizing data which may come from randomly spaced passive pressure sensors.
(2) Description of the Prior Art
The tracking of a high speed (above the incompressible limit, about 0.3 Mach) underwater projectiles with conventional acoustic range systems, several of which are discussed hereinafter, is impractical. For bodies that move at very low Mach numbers, acoustic ranging solutions are convenient. As the sonic speed is approached or reached, conventional acoustic ranging techniques are unreliable. Moreover, the high-speed projectile in relation to the acoustic propagation from the test body creates great difficulty in accurately determining the position from which the acoustic radiation originated.
U.S. Pat. No. 7,283,424, issued Oct. 16, 2007, to Kuklinski, discloses a system and a method to accurately track the trajectory of high-speed underwater objects. A number of hoops with means for controlling the buoyancy thereof are aligned on a range in the anticipated path of the high speed projectile. The hoops are sufficiently large relative to the size of the projectile and anticipated path. Each hoop contains a number of independent hydrophones. The signals from the hydrophones may be analyzed to accurately determine position and track of an underwater projectile along the plane of each hoop. The system may be used as a fixed range or as a mobile range in a remote location.
This patent is limited in many ways. For instance, Kuklinski requires precise acoustic sensor positioning. Kuklinski utilizes an acoustic signal rather than peak pressure signals and times of arrival. Real time solutions are not available. Moreover, Kuklinski does not necessarily provide solutions for a number of desirable variables within a desired error tolerance including ballistic drag and initial velocity (or velocity adjacent the first sensor).
The following U.S. patents describe various prior art acoustic tracking systems:
U.S. Pat. No. 4,639,900 issued Jan. 27, 1987, to Gustafson, discloses three or more listening devices that are dispersed over the water area where the location of a sound source is to be determined and transmit radio signals over respective channels to a master station upon detecting sound. The master station correlates the signals from selected ones of the listening devices to derive the position of the sound source relative to those listening devices. If the positions of those listening devices are unknown, for example if the devices are floating free, their positions are determined by the master station by comparing the relative times at which an identifying radio signal transmitted by each listening device is received by the master station directly and relayed from each of two stationary radio stations with known positions. The listening devices may also be provided with receivers for receiving radio command signals from the master station, for example relating to activation of certain listening devices and assignment of radio channels.
U.S. Pat. No. 5,359,575 issued Oct. 25, 1994, to Williams et al, discloses apparatus and methods for improving signal, detection and tracking in underwater acoustic devices receiving a set of acoustic pulses propagated in response to repetitive synchronizing events. Each pulse is correlated with a replica in a receiver in the underwater devices during an associated time window. The correlated output of the receiver is compared to an adjustable threshold characteristic in a detector for selection of the actual pulse according to predetermined criteria for each of the set of pulses. An actual time of reception relative to the synchronizing event is assigned to the selected pulse. Previous actual times of reception are used to estimate the expected time of reception of the associated pulse relative to the next synchronizing event. The estimate is used to adjust the associated time window to encompass the expected time of reception. Previous actual times of reception are compared to corresponding estimated times of reception to develop a measure of the quality of the estimates. The shape of the threshold characteristic and the width of the associated time window are adjusted as a function of the measure of the quality. A preferred threshold characteristic has a parabolic shape with its vertex defining a minimum threshold level at the expected time of reception. High quality measures lower the minimum threshold and narrow the parabola and the time window; low quality measures raise the minimum threshold level and broaden the parabola and the time window. Adaptive signal tracking is thereby provided.
U.S. Pat. No. 5,377,162, issued Dec. 27, 1994, to Jestin et al, discloses a real time passive trajectography device that comprises at least three pairs of sensors. Each pair of sensors is separated from the other pairs of sensors by a distance which is greater than the distance separating each of the sensors of the pair. Of each pair of sensors, the output signal from a first sensor is used as a reference signal. The output signal from a second sensor is compared to the output signal of the first signal based on a presumed speed of the object being tracked. The presumed speed is continually updated until a maximum correlation between the first and second output signals is obtained. The measurement and correlation operation is repeated at predetermined intervals, with the initial presumed speed extrapolated from the trajectory previously computed during previous intervals. Prior to the speed analysis, the output signals from the sensors are digitized. The output signals are then homogenized and made coherent by a white noise operation to free the information content of the signals from their power throughput. In order to achieve approximate real time operation, a computer for performing the signal analysis includes vectorial cards and has a parallel architecture.
U.S. Pat. No. 5,457,662 issued Oct. 10, 1995, to Forster, discloses a device for locating noise emitters with an antenna comprising passive sensors. In a preferred variant, the antenna consists of N acoustic buoys each comprising a pair of hydrophone dipoles exhibiting a double-eight directivity diagram. Each buoy comprises a compass providing a signal representing the heading relative to magnetic North. The pairs of signals are subjected to a rotation. The signals are next digitized and the number of noise emitters is estimated. The locating of these noise emitters can be performed according to two variants.
U.S. Pat. No. 5,481,505 issued Jan. 2, 1996, to Donald et al, discloses a method and apparatus for detecting, processing and tracking sonar signals to provide bearing, range and depth information that locates an object in three-dimensional underwater space. An inverse beamformer utilizes signals from a towed horizontal array of hydrophones to estimate a bearing to a possible object. A matched field processor receives measured covariance matrix data based upon signals from the hydrophones and signals from a propagation model. A nearest neighbor peak picker provides plane wave peaks in response to output beam levels from the matched processor. A five-dimensional M of N tracker identifies peaks within the specified limit of frequency, bearing change over time, range and depth to specify an object as a target and to display its relative range and depth with respect to the array of hydrophones.
U.S. Pat. No. 6,937,539 issued Aug. 30, 2005, to Kervern et al, discloses processing of signals sent by passive buoys dropped from an aircraft so as to compile EGP (Energy Geographic Plot) maps. The process is split into three steps: the first makes it possible to produce an EGP map of the x, y positions of the noise sources, the second makes it possible to associate the velocities with certain designated positions and the third makes it possible to eliminate the noise sources regarded as hampering the readability of the maps.
U.S. Pat. No. 7,266,044, issued Sep. 4, 2007, to Yang, discloses an apparatus for processing passive acoustic signals received on a horizontal line array that were either emitted from an underwater object or echo returned from an object, and is proposed to track the motion (bearing change and range change) of an object (target) relative to the receiver horizontal line array. Adaptive array processing for a moving object is biased for a moving source when the number of data samples is limited by the stationariness condition. Motion compensation can be carried out in the beam domain by beam shifting for a bearing changing object and frequency shifting for a range changing object. The method includes receiving acoustic signals from the target, determining the beam covariance matrices, determining the target bearing rate and range rate, processing the beam covariance matrices by compensating for the target motion, and producing a beam power plot versus time. Interference signal is suppressed when the interference source does not have the same motion (bearing and range rate) as the target. The method does not need detailed environmental acoustic information of the sound channel normally required to model the sound propagation.
The above cited prior art does not disclose a method to determine the position in space, the position in time, and the track of a traveling underwater body from a set of data which may arise from randomly spaced passive acoustic sensors.
Consequently, those skilled in the art will appreciate the present invention that addresses the above and other problems.